The quadratus plantae (flexor digitorum accessorius) is a unique plantar muscle that attaches to the FDL tendon rather than to bone, modifying the direction of the FDL's pull to redirect it along the long axis of each toe. Because the FDL crosses the midfoot obliquely, its unopposed pull would flex the toes toward the medial side rather than straight down. The quadratus plantae corrects this deviation by pulling the FDL laterally to align toe flexion with the toe's long axis.
| Origin | Medial and lateral plantar surfaces of the calcaneus |
|---|---|
| Insertion | Lateral border of the flexor digitorum longus tendon in the midfoot |
| Nerve Supply | Lateral plantar nerve (S1, S2) |
| Blood Supply | Lateral plantar artery |
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Its directional correction of the FDL pull ensures that toe flexion occurs straight across the MTP joints rather than obliquely, which is essential for effective push-off and prevents toe deformity from oblique flexion forces.
The lateral plantar nerve and artery pass between the quadratus plantae and the flexor digitorum brevis in the second plantar layer. Plantar heel pain from medial calcaneal nerve or lateral plantar nerve entrapment must be distinguished from plantar fasciitis, and the quadratus plantae origin from the calcaneus can be a source of plantar enthesopathy in this region.
The quadratus plantae is not individually palpable as it lies deep in the second plantar layer beneath the FDB. Deep pressure in the mid-plantar foot may produce tenderness in cases of plantar intrinsic muscle pathology.
Stress reaction within the quadratus plantae from excessive barefoot running or intrinsic loading producing deep mid-plantar foot pain distinct from plantar fasciitis, managed with load modification.
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